1. Field
Example embodiments relate to power devices, and more particularly, to Enhancement-mode (E-mode) high electron mobility transistors (HEMTs) and methods of manufacturing the same.
2. Description of the Related Art
A HEMT includes a 2-Dimensional Electron Gas (2DEG) in a channel layer. The 2DEG arises due to a band gap and/or polarizability difference between two layers. For example, a high band gap material may supply carriers to a lower band gap channel layer. The 2DEG is induced at or near the heterojunction of the two layers. Accordingly, the HEMT may include a high mobility channel.
A HEMT may be manufactured as an enhancement mode device in which the HEMT is in a normally off state without applied bias. A normally off HEMT may be manufactured such that a 2DEG is removed from below a gate. Accordingly, the HEMT may operate in an E-mode and its insulation break down voltage may be increased. There are various methods of removing the 2DEG from the channel layer. For example, representative methods include a recess method and a method using a p-GaN layer.
The recess method of manufacturing an E-mode HEMT includes forming a recess at a portion of an AlGaN barrier layer that forms 2DEG in a channel layer. The portion with a recess is an area where a gate electrode is to be formed. With respect to the recess method, damage may occur in a channel layer during processing to form a recess in an AlGaN barrier layer. Additionally, in the case of a recess process for forming an E-mode HEMT with a higher threshold voltage than about 1 V, an on-current of the HEMT may be reduced to less than half.
The method of manufacturing an E-mode HEMT using a p-GaN layer includes forming a p-GaN layer between a gate electrode and an AlGaN barrier layer. With respect to the method using a p-GaN layer, a thickness of an AlGaN barrier layer may be restricted. The thickness of the AlGaN barrier layer should be thin to remove the 2DEG from a channel layer below a gate electrode. However, when the thickness of the AlGaN barrier layer is thin, a concentration of the 2DEG may be reduced in another region of the channel layer outside a region below the gate electrode and an on-current of the HEMT may be reduced.